Device for determining the actinic power of light.



F. M. STEADMAN.

DEVICE FOR DETERMINING THE ACTINICYPOWEH 0F LIGHT.

APPLlcAloN man 1350.221915. RENEwEn Dsc. 13. |911.

Patented Aug. 6, 1918.

A TTH/VEYS FRANK M. STEADMAN. OF CARACAS, VENEZUELA.

DEVICE FOR DETERMINING THE ACTINIC POWER'OF LIGHT. A

Specification of Letters Patent.

Patented Aug'. 6, 1918.

substitute for application serial No.I 871,281, filed november` 1o, 1914. This application filed December-'22, 1915, Serial No. 68,286. Renewed December 13, 1917. Serial N o. 207,018.

10 all whom t may concern.'

Be it known that. I, F RANK M. STEADMAN, a citizen of the United States,- and a resident of Caracas, Venezuela, have invented a new and useful Improvement in Devices for Determining the Actinic Power of Light, of which the following is a speciticatiomthis application being a substitute for my prior application, Serial No. 871,281, filed Nov. 10, 1914.

My invention relates to improvements in devices for determining the actinic power of light, and it consists in the combinations, constructions, and arrangements herein described and claimed.

An object of my invention is to provide a device which may be used in connection with photography to determine the actinic power of the light which is reflected from objects that Aare designed to be photographed.

A- further object of my invention is to provide a device of the type described, which is of relatively small size so that it may be easily transported in the pocket of the user, but by means of which the actinic power may be readily determined.

A further object of my invention is to provide a device of thetype described for determining the actinic power of the light reflected from objects whose light cannot. be conveniently measured directly, by measuring or determining the actinic power of a standard surfaceprovided with a movable part having light and dark portions which may be moved so as to vary theamount of light which is reflected from the surface as a whole.

Otherobjects and advantages will appear in the following specification and the novel features of the device will be particularly pointed out in the appended claims.

My invention is illustrated in the accompanying drawing, forming part of this application, in which- Figure l is a sectional view through the device. r

Fig. 2 is a sectional view on the line 2-2 of Fig. l.

Fig. 3 is a face view of a portion of the standard light retiecting surface or screen.

y Fig. 4 is a face view of the inner containing the lightV openings.

Fig. 5 isa face view 'of' a portion of the sensitive strip showing the discolorations produced by exposure.

In carrying out my invention I provide a receptacle having a back l, a front portion la which, as will be afterward explained, serves as a backing for a sensitized strip, sides lb, and a rear l", which is preferably semi-circular in shape, asshown inthe drawing.

, Arranged to cover f this receptacle is a plate 2 which is provided with a laterally extending portion having a front plate 3', and a partition 4 withtransverse partitions 5 connectingthe plate 3 with the partition 4 and dividing the extension into a series of compartments.

The plate Sis provided with a` series of openings. These openings I have shown at (it, b, c, fl, e, f, but it will'be imderstoodthat a larger or less number' of openings may be provided without. departingV from the spirit of the invention. The opening at is of arbitrary size and is preferably square. The opening Z) is one-half the size of' the openin a-,ibut it will be noted that the length of' the opening b' is the same astliat" ofthe opening a. Similarly the openings c, d', c, f are onehalf of the area of thepreceding' opening'in the order named, the lengths of these openings, however, being precisely the same.' In the roar partition 4 isa seriesl of openings, which in the present instance lare made in the form ofstars but which might'be' made in any suitable shape. These openings I have designated as ct', Z2', 0, d', e, f. They' are situated in alinement with the centers of their respective openings a, .7), etc., inthe opposite wall 3 and each pair ,of openings, such as a, af, is separated fromthe adjacent pair, such as b, 1)', by one ofthe partitions 5.

Hinged at 6 to the extension is a cover 7 which may be moved to cover'the' openings a, b, etc., or swung intothe position shown in Fig. 2 to make an exposure in the manner hereinafter described. It will be observed from Fig. l that this cover' 7 has an extension '7X which projects beyond the device in order to provide a convenient thumb piece portion spring 8 for opening the cover. The cover is hinged as shown in F ig. el: and is provided with a for holding it normally in a closed position so as to shut out light from entering the openings a, Z9, etc. It will be observed that there is a slotor passageway 9 which is left beti'v'een the partition f1 and the side 1, see Figs. 1 and 2, through which the strip 10 may be drawn, this strip 10 consisting preferably of a sensitized band of paper or other suitable material. It will be noted that the strip is carried in a roll on the interior of the receptacle and that it passes out at one side as shown in Fig. 1, the sensitized portion of the strip facing the openings a, Z1', etc.

In Figs. 1, 2 and 3 I have' shown the standard surface. This consists of a frame 12 having upper and lower rollers 18 the axleof one of these rollers being provided with a thumb wheel 1li for turning it. Arranged on the rollers is an endless belt or sheet consisting of a white portion 15 and a black portion 16. At one side of the frame I provide a series of legends indicating the various kinds of objects which may be photographed and whose actinic power may be determined. l

In order to hold the frame 12 at a predetermined distance from the sensitive strip I providethe side members 18, whose ends may be slipped into openings in the frame 12 the opposite ends being retained by means of devices 19 which are provided with sockets to hold the ends of the side members 18.

-From the foregoing description of the various parts of the device, the operation thereof may be readily understood.

Consider now Fig. 1; if one should place his eye at the opening indicatedby the small opening a and look toward the screen, he could just see that portion of the screen which is subtended by the lines and y in Fig. 1 and w and e in Fig. 2. This is substantially the full surface of the screen, so that with the instrument pointed at the screen, no other direct light will be sent to the sensitized lm except that of the screen itself. Of course, if the eye is placed at any of the other openings, the amount of surface which sends direct light is descreased because of the fact that the rectangular opening in front of the star is smaller. rIhus in Fig. 1 the surface which sends its light directly to the opening Z9 through the opening b is that between the lines t and o.

lLet us consider now the measurement of actinic power of the average objects or view whether the day be bright or cloudy or otherwise. The belt is turned so that the dividing line 20 between the white and black portions 15 and 16, respectively, is opposite the-legend average views in Fig. 3. It will be apparent that one-half of the screen will reflect more light than the other half, the amount of reflection being equivalent to the reflection from the average object or view.

The sensitized strip is placed in position in the interior of the receptacle and the plate 2 with its lateral extension is brought into the position shown in Fig. 2, one end of the plate 2 being snapped into engagement with the wall 1c of the casing so as to hold the parts together. The cover 7 is now forced downwardly by means of the thumb and an exposure is .made for any predetermined time. Let us assume that this time is eight seconds. The cover is now released so as to fly back over the openings a, Z), etc., thereby shutting off the light.

The sensitive strip may now be pulled outn wardly, the roll unwinding as the strip moves and after examination the portion of the strip which has been pulled outwardly may be torn off leaving enough, of course, to enable one to pull another portion of the strip out after a subsequent exposure.

The exposure will cause the sensitized strip l0 to be acted on'by the light thereby producing the usual discolorations which are made when a sensitized paper is exposed to the light. These discolorations are shown in Fig. 5 at a, b, and c being progressively fainter. If the day had been .darker then only two of the discolorations, to wit: a and Z2, would have been seen, or if the day had been lighter, there might be other impressions. The dimmest appreciable impression is noted, and the number which corresponds to the opening, corresponde to the discoloration or impression. In this case the number is 32, and, therefore, the actinic power of the object, which in this Case is an average View, in the light which was coming to the object at that time, that is to say, (a bright light, a subdued light, or still less light) is 82. This being known, one may time his exposure for an actinic power of 32.

There must be, of course, a standard unit of actinic power and this standard unit I have chosen arbitrarily as that actinic energy which is produced through an opening of fixed size, as for instance the opening a in 64 seconds of time. In ranging the numbers 8, 16, 32, 64C, etc., opposite the openings a, Z), c, cl, etc., I madean exposure o-f eight seconds and on examining the strip found that only one star or discoloration showed on the strip. If one star shows on an exposure of eight seconds, which is one-eighth of 64, then the amount of light, energy or power which will make this impression or discoloration is eight. The actinic intensity which will make an impression on the paper through the next opening Y) which is onehalf the size of a will, therefore, be 16, the next one 32, the next one 64, and so on.

Right here I desire to call attention to the fact that while the widths `of these Iopenings a, b, c, d, c, and f, are one-half of the preceding opening, the lengths of theseopenings are precisely the same. Keeping one-of the rectilinear dimensions ofthe openings uniform in length-and varying-theirareaby varying their width only enables the following desirable 'result to be obtained. Many objectstobe photographed present -no well extended plain surface, the 'light of which can shine into the actinometer. A distant birds-eye Aview,.a view consisting of all green ,grassV and trees, and Aa group .of flowers, are lthree such objects. As .before explained the white yand black portions of the screen are moved so that the dividing line will coincide with the object to be photographed. .It is onlyby employing rectilinear openings of uniform length and varying width that any .proportion of -black and white will be preserved throughout the series of openings. openings in the .wall-3 are circular or of any .other form than that disclosed.

.0f course, any other standard might fbe used without departing `from the principle of the invention.. The thing to dol is to vassign to the first opening a definite value, and the others will follow as a mat-ter ofcourse.

IVhere an object is near at-'hand and may be measured directly without the use of the endless tape, JI prefer to do so.` Thus lin photographythe lighton the face of the person may befineasured by holdingthe casing containing the sensitive strip up to the cheek and makingthe.eight-second exposure as already described and then determining the actinic powerfby noting the faintest discoloration ontlie strip andtakingthe number opposite it. Thesensitive strip does not need to be held at any given distance from the object-or surface, provided the angleat which-the light comes, is not toogreatto fall outside of the object itself; that is to say,the same result will be accomplished if I hold the device containing the .sensitive .strip an inch away from the cheek or Aone and'onehalf or two inches, because the 4inearer the cheek is approached the less surface sends light to the strip,while the farther laway the moresurface, and, therefore, the action on thestrip is the same. .VVhen, however, the device is held so `far away'that italso takes in Iadjacent parts, :such as the background behind the face, then the trueactinic power ofthe reflected light from Vthe face itself alone, lis not being measured, but only an average measurement of the jface and the background. Y y

A device vof this kind, enables any one, whether skilled in Aphotography `or not, to determine very accurately `the time. of eX- posure and it does away with guess-workffso common in thisgart, thereby insuring good results, and decreasing to a large extent the This is not true .where they possibility of failure due to exposure.

I claim:

l. In a device forfdetermining the actinic power of light, a casing, a sensitive surface Vdisposed 'within the casing, a wall carried by said casing, said wall being' spaced from said sensitized surface and having a series of rectangular openings, the major axes of the sei-ies being parallel and of uniform length and the areas of the openings diminishingV-progressively from one end of th(l over or under series in -simple proportion.

In a device for determining the actinic power of'glight,.a.casing, a sensitive surface disposed withinsaid casing, awall carried by said casing, said wall being spaced from said .sensitizedsurface and Ahaving a series of Arectangular openings, the major aXes of the series being parallel .and vof-uniform length and the areas of the openings diminishing progressively from one end ofthe series in simple proportion, a partition disposed between said sensitized surface and said wall, saidpartition being provided with a 'series of openings of uniform size and arrangedv to register with the centers ofthe respective openings in the series in `the wall.

'3. In a device for determiningvthe actinic power of light, a casing, a sensitive surface disposed within said casing, a wall carried by said casing,said wall being spaced from said sensitized .surface and having la series of rectangular openings, the `major axes of the series being Iparallel and of uniform length .and the areas of the openings diminishingprogressively from one end ofthe series in simple proportion, lapartition disposed Evbetween said sensitized surface and said wall, said .partitionbeing lprovided lwith a series of openings of uniform sizeand arrangedto registerwitht-he centersof the respective openings 'in :the series in :the wall, and a series of transverse partitionsextending 4between said first-mentioned `partition and said wall,the space between any two of said transverse partitions'serving to inclose an openinginthe wall andits vcorresponding opening in thelirst-mentioned partition.

In a device lfordeterminingithe-actinic power of light, a casing, .a sensitive strip disposed within said casing, an extension carried by said `casingand1having.a `partition and va swall, .said partition being arranged to lienorma'llylnext to said sensitized strip and being .provided with a seriesof openingsof.uniform size, the wallof theextension."being,providediwith a series of openn ings correspondingin number to the :firstmentioned series, themaj or axes ofthe openingsiinithe wall being parallel and of aruniform lengtln and Vj the areas of ithe openings in the wall. diminishing progressively ffrom onefend 1o-f fthe .series fin .simple ratio, .and a series of transverse partitions 'between said partition and said wall, the space between any two of said transverse partitions inclosing an opening in the partition and its corresponding opening in the wall.

1n a device for determining theactinic power of light, a casing, a sensitive strip disposed within said casing, au extension carried by said'casing and having a partition and a wall, said partition "being` arranged to lie normally next to said sensitized strip and being provided with a series of openings of iuiiform size, the -wall being provided with a series of openings corresponding Yin number to the lirst-mentioned Serieathemajor :axes of the openings in the wall being parallel and Vof a uniform length, and the areas 0f the openings in the wall diminishing progressively from one end of the series in simple ratio, a series of transverse partitions between said first-mentioned partition and said wall, the space between any two of the said transverse partitions inclosing an opening in the first-mentioned partition, and its corresponding opening in .the wall, and a cover hinged to said casing for shutting oft vthe l` ht from or adn'iitting light to all the openings simultaneously.

G.V in a device for determining the actinie power of light, a casing, a sensitive strip disposed within said easing,` an extension carried by said casing and having a `partition and a wall, said partition being arranged to lie normally next to said sensitized strip and being provided with a series of openings of uniform size, the wall being provided with a series of openings corresponding in number to the first-mentioned series, the major axes of the openings in the wall being parallel and of a uniform length, and the area of the openings in the `wall diminishing progressively from one end'of the series in simple ratio, a series of transverse partitions between said first-mentioned partition and said wall, the space between any two of vsaid transverse partitions inclosing an opening in the first-mentioned partition and its corresponding opening in the wall, a cover hinged to said casing for shutting off the light from or admitting light to all the openings simultaneously, a backing plate, said sensitized strip being arranged to be held between said backing plate and said first-mentioned partition. Y

7. In a device for determining the actinic power of light, a casing, a sensitive strip disposed within said casing, an extension carried by said casing and having a partition and a wall, said partition being arranged to lieJ normally next to said sensitized striprand being provided with a series of openings of uniform size, the wall being provided with a series Vof openings corresponding in number to the first-mentioned series, the major axes of the openings in the wall being parallel and of a uniform length, and the areas of the vopenings in the Wall diminishing `progressively from one end of the series in simple ratio, a series of transverse partitions between said first-mentioned partition and said wall, the space between any two of said transverse partitions inclosing an opening in the first-mentioned partition and its corresponding opening in the wall, a cover hinged to said casing for shutting on the light from or admitting light to all the openings simultaneously, a backing plate, said sensitized strip being arranged to be held between said backing plate and said first-mentioned partition, and a series of numerals corresponding with the series of openings in the nist-mentioned partition and disposed upon that side of the first-mentioned partition which faces the sensitized strip when the latter is in its normal position. Y

8. The combination with a casinO, of a sensitized strip disposed within the casing, a partition and wall carried by said casing, transverse partitions extending between said first-mentionedpartition and said wall, said first-mentioned partition having a series of uniform openings and said wall having a series of corresponding rectangular openings, the major axes of the rectangular openings being parallel andiof uniform length andV the areas of said lastenamed series of openings diminishing progressively from one end of the series, a standard light reflecting surface rigidly secured to said casing. for ren fleeting light through the openings .in the wall, and a movable cover for shutting oli'x the light coming to the outer openings from the light reflecting surface or permitting the entrance of light from the light reflecting surface.

V9. The combination with a casing, of a sensitized strip disposed within the casing, a partition and wall carried by said casing, transverse partitions extending between said first-mentioned partition and'said wall, said first-mentioned partition having a series of uniform openings and said wall having a series of corresponding rectangular openings, the major axes of the rectangular openings being parallel and of. uniform. length and the areas of said last-named series of openingsdiminishing progressively from one end of the series, a standard light reflecting sur- Vface rigidly secured to said casing for reflecting light through the openings in the wall, a movable cover for shutting ofi1 the light coming to the outer openings from the light reflecting surface or permitting the entrance of light from the light reflecting surface, and means for varying the amount of light reflected from the light reflecting surface.

l10. The combination with a casing, of a sensitized strip disposed -withintheeasing 4a partitionfandawall carried by said casing,

transverse partitions extending ,between4 said first-mentioned partition havinga series of uniform openings and said wall having a series of corresponding rectangular openings, the major axes of the rectangular openings being parallel and ofuniformqlength and the areas of said last-named series of openings diminishing progressively from one end of the series, a st-andard light reflecting surface rigidly secured to said casing for reflecting light through the openings in the outer wall, a movable cover for shutting ofi the light coming to the outer openings from the light reflecting surface or permitting the entrance of light from the light reflecting surface, means for varying the amount of light reflected from the light reflecting surface, said last-named means comprising an endless belt having a dark portion and a light portion, and means for shifting the endless belt.

11. The combination with a casing, of a sensitized strip disposed within the casing, a partition and a wall carried by said casing, transverse partitions extending between said first-mentioned partition and said wall, said first-mentioned `partition having a series of uniform openings and said wall having a series of corresponding rectangular openings, the major axes of the rectangular openings being parallel and of uniform length and the areas of said last-named series of openings diminishing progressively from one end of the series, a standard light reflecting surface rigidly secured to said casing for reflecting light through the openings in the wall, a movable cover for shutting olf the light coming to the outer openings from the light reflecting surface or permitting the entrance of light from the light reflecting surface, means for varying the amount of light reflected from the light reflecting surface, said last-named means comprising an endless belt having a dark portion and a light portion, means for shifting the endless belt, a frame for said light reflecting portion, and indicating data on the edge of the frame for indicating the position of the line of division between the dark and light portions of the light reflecting surface for a desired amount of reflection of light.

12. In a. device for determining the actinic power of light, a casingv provided with a partition having a series of light openings of uniform size, a sensitive strip disposed within the casing, means for holding the stri p against one side of the partition adj acent to said openings, a wall carried by the casing and spaced apart from said partition, said wall having a series of rectilinear openings corresponding in number to the open- :rings` in' the partition, ysaid f rectilinear open- -in'gs s varying 1n size, and-transverse parti-V `ti ons v,between `sal d first-mentioned lpartition first-mentioned partition and said Wall, said an'dsaid^avail, said transverse partitionsbe- ,ing disposed between: adjacent openings. Y

13..` Ina'dcvice for determining the actinic vpoiveivoflight, a casing providedwitha partition having a series of light openings of uniform size, a sensitive 'strip -disposed Within the casing, means for holding the strip against one side of the partition adjacent to said openings, a wall carried by the casing and spaced apart from said partition, said wall having a series of rectilinear openings corresponding in number to the openings in the partition, said rectilinear openings being of uniform length and of proportionately decreasing width, and transverse partitions between said first-mentioned partition and said wall, said transverse partitions being disposed between adjacent openings. Y

14. In a device for determining the actinic power of light, a easing provided with 'a partition having a series of light openings of uniform size, a sensitive strip disposed within -the casing, means for holding the strip against one side of the partition adjacent to said openings, a wall carried by the casing and spaced apart from said partition, said wall having a series of rectilinear openings corresponding in number to the openings in the partition, said rectilinear openings being of uniform length and varying in width successively and in simple ratio, and transverse partitions between said firstmentioned partition and said wall, said transverse partitions being disposed between adjacent openings. Y

15. In a device for determining the actinic power ofV light, a receptacle, a Y sensitized strip disposed within said receptacle and adapted to be drawn therefrom, a plate having openings of uniform size, said plate being disposed in close proximity to the sensitive side of the strip, a second plate or wall spaced from the first-mentioned plate and being provided with rectilinear openings corresponding in number and registering with the respectivel openings in the firstmentioned plate, and partitions between said plate for preventing the light coming through one of said rectilinear openings from interfering with that coming through another.

16. In a device for determining the actinic power of light, a receptacle, a sensitized strip disposed within said receptacle and adapted to be drawn therefrom, a plate having openings Vof uniform size, said plate being disposed in close proximity to the sensitive side of the strip, a second plate or wall spaced from the first-mentioned plate and being provided with rectilinear openings p corresponding in number and registering shutting off the light Corning to said recti- 1 with the respective openings 1n the rstlinear openings or for admitting llghtsnnul- Vmentioned plate, partitions between said taneously to said openings.

plate for preventing the light coming .f FRANK M.STEADMAN.

5 through one of said rectilinear openings lVVitnesSes:

from lnterfering with that connng through C. O. BERTSGHE, another, and a cover for snnultaneously J. ODELL FOWLER.

Qopies 'of this patent may be obtained for ve cents each, by addressing the Commissioner of Yatents, Washington, D. C. 

